The present invention relates to a system for the introduction of fuel in a multi-cylinder combustion engine.
To provide an accurate dose to each of the cylinders, it is known that, a therein fitted common gas supply is used and that, with the help of a cut-off valve with various grooves, each of the cylinders is separately supplied with an accurately dosed quantity of gas, wherein the position of the grooves are electrically controlled and determine how much gas is injected. If such a system is connected in closed loop with a xcex-probe, the present environmental requirements can be met. An example of this can be found in the European patent 0.563,223.
However, increasingly higher requirements are being put on the optimal fuel mixture, under changing circumstances. This can include the changing of the number of revolutions, for example, and the load of the internal combustion engines.
In gasoline driven internal combustion engines, controls have been developed for the intermittent or sequential introduction of (liquid) gasoline. If intermittent control takes place at an equal or higher frequency than the camshaft revolutions of the combustion engine, this control offers the possibility of supplying the optimal quantity of fuel for each combustion cycle, This is because the period required for the fuel supply is shorter than the cycle time of the combustion engine. During the switching on and off of the fuel supply, problems can occur, however, in supplying the correct quantity of fuel to the separate cylinders. By simultaneously switching the fuel supply of several cylinders on or off one or more of the cylinders receives only a part of the required fuel, whereby an incorrect mixture can result. If the control is completely sequential, that is, for each separate cylinder the correct quantity of fuel at the correct time, then the dose can also be correctly supplied during the switching on and off of the fuel supply.
Apart from the advantage when starting and switching off, further reductions in the emissions are achieved by sequential control by the introduction of the fuel taking place at the most optimal time for the particular cylinder.
From the xe2x80x98SAE Technical Paper Seriesxe2x80x99 951913 xe2x80x98Ultra Rapid Natural Gas Port Injectionxe2x80x99, a multi-point sequential injection system for natural gas (methane) is known. The injector used there has a disk formed metallic valve which is operated by a coil,
Such a system functions only with a comparatively high pre-pressure (several bars), requires a considerable electrical power whereas the wear is not negligible and is higher than the lifetime of the other engine components. The dimensions of the coil, in particular, are a hindrance to realizing this construction. After all, in the modern combustion engine there is limited space available for (afterwards) fitting of injectors for gaseous fuel and a there must be a significant freedom in the installation position. By intermittently or sequentially injecting greater freedom is achieved with respect to the valve timing and manifold geometry.
The object of the present invention is to avoid the above mentioned disadvantages.
It has been found that with a comparatively simple auxiliary/main valve-construction, switching is possible at particularly high frequencies, without non-permissible deviations from the opening characteristic of the main valve occurring. This construction also gives a greater freedom with regards to the seating dimensions of the main valve and to the working pressure.
It is noted that from the Dutch application 9101106 a dosing valve is known for pneumatic purposes. There, an auxiliary valve is used which is connected on one side to the gas outlet. The other side of the auxiliary valve is not directly connected to the gas supply, but a membrane is connected in between. It is assumed that by the under-pressure in the outlet when the auxiliary valve is open, the membrane is sucked away from the supply so that a greater supply is released. From that known construction the membrane closes off two small pipes which are connected via a channel with the other side of the membrane and so provides the control. It is therefore possible that, during the closing movement of the membrane to the small pipes in particular, a time-lag effect is created which can culminate in a strutter behavior.
Such a construction is aimed for central introduction of fuel with a mixer, whilst the subject application aims the use of one or more injectors for each cylinder (multipoint injection).
According to a further advantageous embodiment of the invention, a controller is present for the separate control of each of the dosing valves depending on the operational conditions of that internal combustion engine.
According to an advantageous embodiment of the invention the auxiliary valve is directly connected on one side with the gas supply and on the other side to the gas outlet, wherein the volume of the main valve is connected with the gas supply through a restriction, More particular the main valve comprises a membrane controlled valve, wherein on one side of the membrane the gas supply pressure acts through a restriction and wherein over a part of the other side of the membrane the same gas supply pressure acts and on a further part of said other side the gas outlet pressure applies.
According to a further advantageous embodiment, the gas outlet of the main and auxiliary valves is shared.
The membrane can comprise any material known in the art and in particular rubber materials are preferred. The auxiliary valve can be any valve known in the state of the art, such as a needle valve or a disc valve.
According to an advantageous embodiment of the invention, the main valve and auxiliary valve are made such that a maximum of 30% of the total amount of gas flows through the auxiliary valve and a minimum of 70% through the main valve.